a) Field of the Invention
This invention relates to a data carrier identification system, and more particularly, to a data carrier identification system which employs a communication controller for reading and writing data from and into one or more data storing unit(s) which carry data for the control of production lines, conveyor systems, room access control, the movement of livestock, etc.
b) Discussion of the Related Art
Identification systems, which read or write data from and into a data storing unit (hereinafter data carrier) from a controller and using electromagnetic induction, radio waves, or light rays are known. A data carrier including a semiconductor memory such as an EEPROM or SRAM (Static RAM) is mounted on articles which are moved, for example, on a production line. After an article comes into an area where data communication with the controller is possible, the controller begins to communicate with the data carrier using, for example, a reading/writing head.
During data reading, the controller transmits a command code, and a read command including an address to a data carrier. The data carrier reads data from its storage unit in response to the read command and transmits the data to the controller. During data writing, the controller sends a command code, and a write command including an address and the data to be written. The data carrier writes the data into its storage device in response to the write command.
In this system, if more than one data carrier is present in an area where data communication with the controller is possible, correct data communication is difficult because a data carrier which is expected to communicate with the controller cannot be differentialed from other data carriers in the same vicinity. Accordingly, to achieve correct communication, objects must be controlled to enter a communication area one-by-one, and accurate positioning of the read/write head of the controller is required.
In addition, for the control of people entering and leaving a room, a path and a gate are required for guiding people one-by-one into a communication area. This is also true for livestock control. Additional devices or facilities are thus required for correct communication.
c) Summary of the Invention
It is, therefore, an object of this invention to provide a data carrier identification system in which a controller can correctly communicate with a data carrier, even if more than one data carrier is present in a communication area.
According to this invention, a data carrier identification system is provided in which different data carrier numbers (DCNos.) are assigned to different data carriers in a communication area where data communication with the controller is possible. The different DCNos. allow easy and correct access by the controller to a specific data carrier which is expected to communicate with it, even if more than one data carrier is present in a communication area.
When a data carrier newly entering the communication area has a data carrier number which is the same as the data carrier number of a data carrier already in the area a controller causes a change in the data carrier number of at least one of conflicting data carriers so that no two data carrier numbers have the same data carrier number.